Rhepoxynius tridentatus (J. L. Barnard 1954)

Rhepoxynius tridentatus (J.L. Barnard)

Pontharpinia tridentatus.—J.L. Barnard, 1954:4–6, pls. 4, 5.

Paraphoxus tridentatus.—J.L. Barnard, 1960:261–265, pls. 38, 39 [including subspecies p. t. pallidus]; 1966a:90; 1969:224.

DESCRIPTION OF FEMALE.—Female “b,” 7.81 mm: Head about 18 percent of total body length, greatest width about 90 percent of length, rostrum constricted, narrow, short, reaching middle of article 2 on antenna 1. Eyes small to medium, clear of pigment (long preseved), ommatidia ordinary. Article 1 of peduncle on antenna 1 about as long as wide, about 2.8 times as wide as article 2, ventral margin with about 5 setules, weakly produced dorsal apex with 4 setules-setae, article 2 about 0.8 times as long as article 1, with ventral cycle of 10 widely spread setae, and 2 lateral setae; primary flagellum with 10 articles, about 0.7 times as long as peduncle, bearing 1 each short aesthetasc on articles 3–9, accessory flagellum with 9 articles. Antenna 2 ensiform; facial setae of article 3 closely contiguous and subequally long (unusual); spine formula of article 4 = 3–4–6, dorsal margin with 2 notches bearing 3 setae each, ventral margin with 13 groups of 1–2 long to short setae, plus 3 ventrodistal long setae and 1 facial spine, article 5 about 0.85 times as long as article 4, facial spine formula = 4, dorsal margin bearing 2 sets of long setae, ventral margin with 6 sets of 1–2 long to medium setae, 3 ventrodistal long to medium spines set facially; flagellum about 0.95 times as long as articles 4–5 of peduncle combined, with 12 articles.

Upper lip and epistome distinct, upper lip dominant and upper edge forming weak anterior cusp from lateral view. Mandibles with weak palpar hump, right incisor with 3 teeth, third highly apical, left incisor with 2 sharp teeth in 2 branches, distal with tiny accessory hump; right lacinia mobilis bifid, distal branch little shorter than proximal, narrow, proximal branch simple, pointed, left lacinia mobilis very broadly flagellate, with 5 teeth plus 2 accessory teeth, middle teeth shortened; right rakers 11, left rakers 13; molars composed of elongate plaques bearing short protrusion, right molar with 7–8 long to medium spines, no spine disjunct, left molar with 4 primarily long spines plus 1–2 spines weakly disjunct, no molar with plume; palp article 1 short, article 2 with 1 short inner apical seta and 3 other short inner setae, and 5–6 long outer setae in 3–4 sets, article 3 about as long as article 2, oblique apex with 16 spine-setae, basofacial formula = 0–4. Each outer lobe of lower lip with tiny cone. Inner plate of maxilla 1 especially thin, bearing 1 medium apical pluseta, 1 similar apicomedial seta, 2 apicolateral slightly shorter setae, palp article 2 with 1 apical spine, 1 apicolateral, 5 medial and 9+ submarginal setae. Inner plate of maxilla 2 shorter than outer, outer broader than inner, outer with 2 apicolateral setae, inner with 4 medial setae. Inner plate of maxilliped with 1–2 large thick apical spines, 2 apicofacial setae, 6 medial setae, outer plate with 6 medial spines, no apicolateral setae or cusp, palp article 1 with 3 lateral setae, article 2 with 4 groups of 9 lateral setae, medial margin of article 2 moderately setose, article 3 with 9 strewn facial setae, 3 lateral setae, nail of article 4, short, almost completely fused, with 2 accessory setules.

Coxa 1 scarcely expanded apically, anterior margin weakly convex, straight, main ventral setae of coxa 1–4 = 10–14–12–11, moderately widely spread, posteriormost seta of coxae 1–4 as long as others; anterior and posterior margins of coxa 4 weakly divergent, posterior margin oblique, convex, posterodorsal corner rounded, posterodorsal margin ordinary, concave, width-length ratio of coxa 4 = 7:8.

Gnathopods generally ordinary, but hands thin, moderately setose anteriorly, width ratios on articles 5–6 of gnathopods 1–2 = 22:19 and 22:19, length ratios = 65:40 and 61:40, palmar humps small, palms transverse, article 5 of gnathopod 1 elongate, ovate, posterior margin rounded, long, article 5 of gnathopod 2 elongate, ovate, posterior margin flat, long.

Pereopod 4 stouter than pereopod 3 especially on articles 4–5, facial setae formula on article 4 = 10 and 15, parallel to apex, on article 5 = 8 and 6, main spine of article 5 extending to M. 75 on article 6, article 5 with no proximoposterior spines, spine formula of article 6 = 7 + 8 and 7 + 10 plus no middistal seta, some spines especially long, acclivity on inner margin of dactyls of pereopods 3–4 weak, emergent setule short, midfacial pluseta ordinary. Coxae 5–7 posteroventral seta formula = 6–21–1. Articles 4–5 of pereopods 5–6 of ordinary width, facial spine rows dense, facial ridge formula of article 2 on pereopods 5–7 = 0–1–1; width ratios of articles 2, 4, 5, 6 of pereopod 5 = 64:51 :49: 18, of pereopod 6 = 87:48:33:14, of pereopod 7 = 90:22:18:8, length ratios of pereopod 5 = 101:49: 45:40, of pereopod 6 = 103:72:47:55, of pereopod 7 = 100:27:23:22, article 2 of pereopod 7 reaching middle of article 4, posterior margin with 4 large and 1 small serrations, medial and lateral apices of articles 5–6 finely combed, article 6 lacking digital processes.

Posteroventral corner of epimeron 1 rounded, posterior margin convex, anteroventral margin with 10 long to medium setae, posteroventral face with 2 long setae set obliquely. Posteroventral corner of epimeron 2 rounded, posterior margin strongly convex, ventral marginal and facial setae = 21, posteriormost triad set vertically. Posteroventral corner of epimeron 3 rounded, weakly protuberant, posterior margin almost straight, with 2 setae and 1 setule notch, ventral margin with 6 setae mainly posterior but widely spread, face with 2 setae near ventral posterior margin.

Urosomite 1 without lateral or ventral setule at base of uropod 1, articulation line almost complete, urosomite 3 unprotuberant dorsally. Rami of uropods 1–2 with articulate but tightly fixed apical nails, outer ramus of uropod 1 with 1 small dorsal spine, inner with 1 larger, outer ramus of uropod 2 without dorsal spines, inner with 1 dorsomedial spine. Peduncle of uropod 1 with 5 basofacial setae and 2 apicolateral spines, and 1 tiny more proximal seta, medially with 4 marginal thin setae and 1 thick apical spine. Peduncle of uropod 2 with 1 basofacial seta!, and 6 even dorsal spines, basalmost thinner, medially with 1 large apical spine, apicolateral corners of peduncles on uropods 1–2 with no comb. Peduncle of uropod 3 with no ventral spines, dorsally with no lateral spine or setule, 1 medial setule, rami feminine, inner extending to M. 70 on article 1 of outer ramus, apex with 1 seta, medial and lateral margins naked, article 2 of outer ramus short 0.15, bearing 2 medium setae, medial margin of article 1 with 5 setae, lateral margin with 4 acclivities, spine formula = 0, short setal formula = 1–1–1–1–1, long setae = 0–1–1–1–1. Telson especially long, length-width ratio = 3:2, almost fully cleft, each apex of medium width, rounded, lateral acclivity deep, narrow, bearing ordinary lateral setule, seta next medial shorter than setule, midlateral setules diverse, larger of medium size.

DESCRIPTION OF MALE (young male “c,” 5.66 mm).—Setae on article 2 of antenna 1 not as widely spread as in other described specimens; outer ramus of uropod 1 lacking spine.

MATERIAL.—USNM Acc. 187867, False Bay, San Juan Island, Washington, eastern Pacific Ocean, coll. Margaret Dunn, 1 July 1950, female “b,” 7.81 mm, young male “c,” 5.66 mm (re-identified, formerly identified in USNM colls. as “milleri”); 163372, False Bay from burrows of Leptosynapta inhaerens?, coll. G.E. MacGinitie, 1 August 1940 (20). AHF Velero IV 4797–56, southern California, 20 m (2 specimens of 3-cuspidate form with widely spread first antennal setae lacking last setal position, thus normal tridentata).

RELATIONSHIP.—See R. heterocuspidatus. Rhepoxynius tridentatus is the northern race or morph of R. heterocuspidatus, but R. tridentatus nomenclaturally takes priority; however, there may be fairly good genetic distinction, because the mixture is fairly sharp as shown in male “c” quoted above. More research on these species is warranted.

FOUR-TOOTH FORM.—False Bay P. t. pallidus specimens from USNM Acc. 163372 have 4 posterior teeth on article 2 of pereopod 7, but unlike R. heterocuspidatus they are formed evenly. Juveniles have the 3 teeth of the open-sea morphs.

DISTRIBUTION.—Puget Sound, Washington, to vicinity of Point Conception, California, 0–89 m; form of Bahí de Los Angeles, Baja California, reported by J.L. Barnard (1969) needs further study; R. tridentatus probably including R. heterocuspidatus, thus distribution extending normally into Gulf of California.